1. Field of the Invention
The present invention relates to a feed roller used for developing devices in image-forming apparatuses such as copying machines and for powder-mixing apparatuses.
2. Description of the Related Art
Heretofore, as a mixing roller for mixing a developer in developing devices arranged in image-forming apparatuses or as a feed roller for feeding the developer to a developing roller, the following rollers have been devised:
a. A vibration-type mixing roller whose spiral-shape mixing wing has a cutout as shown in FIG. 1 (Japanese Laid-open Patent Publication No. 197026/1986);
b. A screw-type spiral roller as shown in FIG. 2 (Japanese Laid-open Utility Model Publication No. 87735/1987);
c. A mixing roller having a mixing wing parallel to a rotating shaft thereof and a spiral groove to prevent pressure rise as shown in FIG. 3 (Japanese Laid-open Utility Model Publication No. 47353/1988);
d. A roller having a feed roller with a flat wing and including a spiral roller near the feed roller as shown in FIG. 4 (Japanese Laid-open Utility Model Publication No. 184068/1985);
e. A feed roller having an opening located on the backward section with respect to the rotating direction of a spiral-shape mixing wing as shown in FIG. 5 (Japanese Laid-open Utility Model Publication No. 53459/1987); and
f. A feed roller having a spiral wing having a rectangular plane member as shown in FIG. 6 (Japanese Laid-open Utility Model Publication No. 140969/1985).
However, among the above-described mixing rollers or feed rollers, the spiral-shape rollers as shown in the items a, b and e have had a problem that they have a small capability to feed a developer to a developing roller, and the roller having an auxiliary lateral-feed mechanism as shown in the item d or the one having a mixing wing parallel to a rotating shaft thereof as shown in the item c have a problem that they have a poor lateral mixing performance and particularly the one of spiral-shape as shown in the item f has a problem that they scrape up developer diagonally to a developing roller.
Also, as an another type of roller, a roller having a shaft and lateral-feed blades mounted on the shaft is available. The lateral-feed blades are designed to laterally feed a developer and mix the developer so as to keep proper fluidization balance of the developer. For example, as disclosed in Japanese laid-open Patent Publication No. 21468/1989, a roller is known in which the screw pitch of lateral-feed blades S is made large on the start side in the screw-conveyance direction and small on the end side (see FIG. 7).
However, such prior art mixing rollers have had a problem that, since their lateral-feed blades are continuous spiral-shape blades, when an attempt is made to change variously their pitch with shaft position, the density of blades at a place of large pitch becomes inevitably coarse, thereby causing the developer lateral-feed force not to be increased.